1. Field of the Invention
The present invention relates to a motor and a method for manufacturing the motor and more particularly, to a technique for effectively winding a wire for forming an armature winding, between a commutator and an armature.
2. Description of the Related Art
In a known DC motor, the same number of brushes as the number of poles of a stator is provided. However, the resistance loss caused by friction between a commutator and the brushes during rotation of an armature may increase with increase in the number of brushes. Further, the number of parts increases as the number of brushes increases. In this connection, Japanese non-examined laid-open Patent Publication No. 2-184246 discloses a motor which can be driven while having a four-pole stator and two brushes by connecting diametrically opposed segments of a commutator by an equalizing wire such that the coils connected to the opposed segments are electrically equalized.
According to a known method of forming a wire connection (hereinafter referred to as “unit winding”) including two electrically equalized coils and an equalizing wire, one of the coils is formed by winding a wire connected to a starting-point segment, around a predetermined slot group of slots, the other coil is subsequently formed by winding the wire around a slot group of slots which is diametrically opposed to said slot group. Then, the equalizing wire is formed by connecting the wire from the other coil to a relay segment and then to an endpoint segment. Further, unit windings of the same kind are formed by repeating the above-mentioned procedure, while shifting the starting-point segment by one segment in the circumferential direction around the axis of the commutator. Thus, the two coils of each of the unit windings are successively formed while shifting one slot in the circumferential direction around the axis of the armature. In this manner, an armature winding is formed between the armature and the commutator.
In such a case, the wires are sequentially connected in a regular manner from a segment which is shifted by one segment in the circumferential direction around the axis of the commutator, to a slot which is shifted by one slot in the circumferential direction around the axis of the armature. As a result, the wires connected between the commutator and the armature tend to regularly overlap each other, so that imbalance in the wire volume is created. As a result, the rotor, which is formed by the output shaft, the armature, the commutator and the armature winding, has an imbalance in weight and thus the center of rotation of the rotor tends to be displaced from the output shaft.